The present invention generally relates to machines for extruding food products from, e.g., corn meal. More specifically, the invention relates to machines for extruding food products as described in U.S. Pat. Nos. 2,295,868 and 2,350,643.
In U.S. Pat. Nos. 2,295,868 and 2,350,643, both of which are incorporated herein by reference, there is described a machine and process for preparing extruded food products wherein raw material such as corn meal is reduced to a cooked fluid under considerable pressure, the food being left more or less tenacious and containing innumerable infinitesimal particles of water or vapor. The machine is designed to be self-heated by friction between particles of food matter and between the particles and surfaces of contacting metal in a manner such that pressure is progressively built-up during the heating period.
Uncooked raw material having a predetermined moisture content is processed into a somewhat viscous liquid having a temperature that is high enough to cook the material and to cause the water particles to evaporate at atmospheric pressure. However, because the material is under pressure, the water does not evaporate within the machine.
To provide the raw material with moisture, it is humidified, then broken down and cooked under pressure, as described above. During cooking, it is agitated to a point where it takes the form of a fluid but having sufficient viscosity to expand into a cellular structure when the pressure is released.
To accomplish the foregoing, after the material is cooked and liquefied, the material is extruded between two very closely spaced annular smooth surfaces, one of which turns at a relatively high speed, a rotor, the other of which is stationary, a stator, thereby to cause the material to whirl as it is extruded between these surfaces into atmospheric pressure. The expansion of pent up vapor and release steam forms cells in the extruded material thereby to form a cellular structure. The cellular structure is exuded from the machine in the form of a stream.
This machine has been produced and used in the United States for many years, as these patents issued in 1939. The basic design has remained relatively unchanged since then.
In the operation of the machine described above, the grain is manually humidified and then manually fed into the extruder. An operator then manually sets the gap between the rotor and stator, starts the drive motors, and after a preheat period, resets the gap until the resultant product appears to be at the proper density and appearance. This procedure is not exact, since there are no measuring devices on the machine to show this information. Therefore, start-up and operation of such machines varies from time-to-time and operator-to-operator.